This invention relates to improved jacking mechanisms for lowering a well pipe such as a casing into a well bore.
In wells of substantial depth, the weight of the casing which is required to line the well can become very great, and may exceed the load capacity of a rig mast and other related equipment which are otherwise satisfactory to meet all requirements of drilling the well and placing it in production. For example, a mast and other equipment having a 500 ton capacity may be entirely adequate for handling the drill pipe and other equipment employed in drilling a well, but may be of insufficient capacity to suspend and progressively lower the relatively large diameter casing which must ultimately be positioned in the well. To employ a mast and other equipment of heavier capacity, for example with a 1,000 ton load limit, during the entire drilling operation, is economically inefficient, but may be necessary unless other means are provided for lowering the casing.